The present invention relates to an adjusting method for a roller section of a continuous casting machine which is provided with a section input side and a section output side and a pair of roller carriers which each carry at least two rollers extending over a supporting zone, with the roller carriers being mutually adjustable towards one another by means of an adjusting unit arranged at the section input side and section output side, with each adjusting unit being provided with hydraulic cylinder units on either side of the supporting zone.
Such an adjusting method is known from DE 196 27 336 C1 for example.
During the continuous casting of metal for example, and during the casting of a steel strip in particular, the solidifying billet is drawn off and supported via a roller course with a plurality of supporting rollers. In order to ensure the precisest possible guidance of the billet, the roller course is broken down into several sections according to DE 196 27 336 C1 which can be adjusted separately.
Bellying can occur in the still cast-heated metal billets, which moreover are not yet solidified in the core region. When such a bellying passes through a roller section, an even larger force than usual is exerted on the section. This may under certain circumstances lead to damage to the roller section. Moreover, the bellying must be compensated again during the further processing of the metal billet.
It is the object of the present invention to provide an adjusting method by means of which damage to the roller section as a result of excessive exertion of force can be avoided in any case and, moreover, bellying can be eliminated to the highest possible extent.
This object is achieved in such a way that the hydraulic cylinder units are adjustable both in a position-controlled as well pressure-controlled manner, that the rollers are moved via the hydraulic cylinder units in a position-controlled manner towards a metal billet which is supported by the same and that the hydraulic cylinder units can be changed over from position-controlled to pressure-controlled operation when the pressure in the respective hydraulic cylinder unit reaches a hydraulic cylinder threshold value.
Preferably, a hydraulic cylinder unit will also be changed over from a position-controlled to a pressure-controlled operation when the pressure in the other hydraulic cylinder unit of the same adjusting unit reaches the hydraulic cylinder threshold value. This substantially causes a synchronism between the two hydraulic cylinder units of each adjusting unit.
Any overload of the rollers can be avoided in a simple manner when the hydraulic cylinder units of an adjusting unit are changed over from a position-controlled to pressure-controlled operation when the sum total of the pressures in the hydraulic cylinder units of the adjusting unit reaches an adjusting unit,threshold value.
Similarly, an overload of the roller section can be avoided when all hydraulic cylinder units of the roller section are changed over from position-controlled to pressure-controlled operation when the sum total of the pressures in the hydraulic cylinder units reaches a section threshold value.
In an embodiment of the present invention the adjusting unit produces after the changeover from the positional control to pressure or force control a permanent form closure between the metal billet and the rollers. As a result of this measure, bellying of the metal billet and, optionally, its break-out are avoided. The form closure between the metal billet and the rollers ensures the rotation of the rollers and thus their optimized cooling. Moreover, the form closure produces the continuous conveyance of the metal billet between the rollers.
The hydraulic cylinder threshold value, the adjusting unit threshold value and the section threshold value are preferably parameterizable in order to enable the adjustment to the constructional conditions of the roller section.